The present invention relates to a method and apparatus for performing multilayer film deposition on a substrate surface, e.g., a disk-shaped substrate, which method and apparatus utilizes a side-loading, multiple linear magnetron cathode sputtering device. The invention has particular utility in the formation of multilayer superlattice structures, e.g., (Co/Pt)n and (Co/Pd)n superlattices, as part of automated manufacture of magnetic and magneto-optical (MO) data/information recording, storage, and retrieval media in disk form.
Magnetic and magneto-optical media are widely employed in various applications, particularly in the computer industry for data/information storage and retrieval purposes. A conventional, single-sided, longitudinal magnetic recording medium 1 in e.g., disk form, such as utilized in computer related applications, is schematically depicted in FIG. 1 and comprises a non-magnetic substrate 10, e.g., of glass, ceramic, glass-ceramic composite, polymer, metal, or metal alloy, typically an aluminum (Al)-based alloy such as aluminum-magnesium, having at least one major surface on which a layer stack comprising a plurality of thin film layers constituting the medium are sequentially deposited. Such layers typically include a plating layer 11, as of amorphous nickel-phosphorus (NiP), a polycrystalline underlayer 12, typically of chromium (Cr) or a Cr-based alloy, a magnetic recording layer 13, e.g., of a cobalt (Co)-based alloy, a protective overcoat layer 14, typically containing carbon (C), e.g., diamond-like carbon (DLC), and a lubricant topcoat layer 15, typically of a perfluoropolyether compound.
Magneto-optical (MO) recording media (MO) similarly comprise a laminate of layers formed over a suitable substrate, e.g., a disk. By way of illustration, shown in FIG. 2 is a single-sided MO medium 20 having a first surface magneto-optical (FSMO) layer configuration, wherein reference numeral 21 denotes a disk-shaped substrate formed of a material selected from, for example, aluminum (Al), plated aluminum, aluminum alloys, metals, metal alloys, glass, ceramics, and glass-ceramic composite materials. Formed on one surface 21A of substrate 21 is a layer stack, comprising, in sequence from surface 21A, a reflective, heat sinking layer 22, comprising Al or an alloy thereof, e.g., AlCr, AlTi, AlCu, AlMo, etc., which layer may also serve to prevent laser beam transmission through the substrate when the latter is transparent, as in the case of glass or glass-based materials, and thus render surface 21A opaque; a first dielectric material layer 23, substantially transparent to the wavelength(s) of the at least one laser beam employed for writing and reading out information stored in the medium, typically selected from SiNx, AlNx, SiOx, and AlOx; a MO read-write layer 24, for example, comprising a rare earth-transition metal thermo-magnetic (RE-TM) material having perpendicular magnetic anisotropy, large perpendicular coercivity Hc at room temperature, and high Curie temperature Tc, typically selected from TbFe, TbFeCo, TbDyFeCo, etc.; a second transparent dielectric material 25 typically selected from the same materials utilized for the first transparent dielectric layer 23; a thin, amorphous, diamond-like carbon (DLC) protective overcoat layer 26; and a lubricant topcoat layer 27, typically comprising a fluoropolyether or perfluoropolyether material.
A promising new class of materials suitable for use as the magnetic recording layer 13 of the magnetic medium of FIG. 1 or the MO read-write layer 24 of the magneto-optical (MO) medium of FIG. 2 includes cobalt/platinum (Co/Pt)n and cobalt-palladium (Co/Pd)n multilayer stacks, also referred to as xe2x80x9csuperlatticexe2x80x9d structures. As schematically illustrated in FIG. 3, such multilayer stacks or superlattice structures 30 comprise n pairs of alternating discrete layers of Co (designated by letter A in the drawing) and Pt or Pd (designated by letter B in the drawing), where n=an integer between about 10 and about 30. Superlattice 30 is typically formed by a suitable vapor deposition technique and can exhibit perpendicular magnetic anisotropy arising from metastable chemical modulation in the direction normal to the substrate. Compared to conventional cobalt-chromium (Coxe2x80x94Cr) alloys utilized in magnetic data storage/retrieval disk applications, such (Co/Pt)n and (Co/Pd)n multilayer or superlattice structures offer an economic advantage in facilitating room temperature deposition processing necessary for utilization of lower cost polymeric substrates. When utilized in MO disk-based applications, (Co/Pt)n and (Co/Pd)n superlattices offer superior corrosion resistance and blue wavelength response vis-a-vis conventional RE-TM alloys.
For example, a (Co/Pt)n multilayer stack or superlattice 30 suitable for use as the magnetic recording layer 13 of the magnetic recording medium of FIG. 1 or the magneto-optical (MO) read-write layer 24 of the MO medium of FIG. 2 can comprise a plurality of Co/Pt pairs, i.e., n=about 10 to about 30, e.g., 13, wherein each Co/Pt pair consists of a 3-5 xc3x85 thick Co layer adjacent to an 8 xc3x85 thick Pt layer, for a total of 26 separate or discrete layers. When utilized as a high recording density magneto-optical (HDMO) read-write layer 24 in e.g., a MO medium as illustrated in FIG. 2, such multilayer stacks or superlattice structures 30 are characterized by having a large perpendicular anisotropy and high coercivity, high squareness ratio (S) for a magnetic hysteresis (M-H) loop measured in the perpendicular direction, and high Kerr rotation angle for light of a particular wavelength region, e.g., blue or red light. By way of illustration, but not limitation, (Co/Pt)n and (Co/Pd)n HDMO superlattices, wherein n=about 10 to about 30 pairs of Co and Pt or Pd layers having thicknesses as indicated supra and fabricated, e.g., by means of techniques disclosed in U.S. Pat. No. 5,750,270, the entire disclosure of which is incorporated herein by reference, exhibit perpendicular anisotropy exceeding about 2xc3x97106 erg/cm3; coercivity as high as about 5,000 Oe; squareness ratio (S) of a M-H loop, measured in the perpendicular direction, of from about 0.85 to about 1.0; and carrier-to-noise ratio (CNR) of from about 30 dB to about 60 dB.
According to conventional methodologies and practices for automated manufacture of disk-shaped magnetic and MO media, when the various above-described thin film layers constituting the medium are deposited on the disk-shaped substrates, as by cathode sputtering techniques, it is generally advantageous to coat one disk at a time with the various requisite layers. However, the continuing requirement for increased storage density has increased the number of requisite layers and, as the number of requisite layers increases, it becomes impractical to build and operate linearly arranged, multi-chamber cathode sputtering apparatus wherein each separate or discrete layer to be deposited requires a separate vacuum chamber, because the resulting system becomes unwieldy as a result of its great length.
The above-described difficulty associated with increasing numbers of requisite layers is magnified in the case of recording media comprising (Co/Pt)n or (Co/Pd)n multilayer stacks or superlattice structures where n=about 10 to about 30 layer pairs, due to the very large number of individual layers required to be deposited. Currently available disk processing apparatus, whether pallet pass-by, single disk, or some variation thereof, do not have an adequate cathode count for single-pass coating of a large number of layers. Certain types of existing sputtering apparatus can be modified to perform multiple pass, back-and-forth, or up-and-down repetitive disk transport to fabricate multilayer stacks with a limited number of sputtering cathodes, but such reduction in cathode number incurs a significant reduction in productivity, hence increased manufacturing cost.
Moreover, to date, no production-type sputtering system based upon such modification of existing sputtering apparatus, is capable of performing multilayer deposition on 95 mm diameter disks with a required radial film uniformity (e.g., +/xe2x88x923% thickness variation).
Other types of existing sputtering apparatus, e.g., the Intevac MDP 250 style frequently utilized for magnetic and MO recording disk manufacture, transport each disk with an intermittent up-and-down motion which can be exploited for reducing the requisite number of coating stations; however, the required number of sputtering cathode/target assemblies cannot be reduced.
It is therefore considered that a method and apparatus for forming multilayer stacks or superlattice structures which minimizes the requisite number of sputtering cathode/target assemblies without sacrificing productivity is required for realizing economically viable manufacture of (Co/Pt)n and (Co/Pd)n superlattice-based magnetic and/or MO recording media. One possible approach for achieving such result is to utilize nested, annularly-shaped, independently powered Co and Pt or Pd sputtering cathodes/targets which can be alternately energized to sputter discrete layers of Co and Pt or Pd to form a multilayer stack. However, this approach entails several drawbacks, e.g., fabrication of the annularly-shaped targets is expensive, the cathode/target structure is mechanically complex, and control of the film thickness and properties in the radial direction is limited, resulting in excessive radial non-uniformity, as for example, shown in FIG. 4.
Accordingly, there exists a need for improved means and methodology for forming, as by cathode sputtering, multilayer stacks or superlattice structures, for use in e.g., single- and dual-sided magnetic and/or MO data/information storage and retrieval media in disk form, which means and methodology form part of a multi-station processing apparatus and enable rapid, simple, and cost-effective formation of such media.
The present invention, wherein multilayer or superlattice structures are formed in a side-loading sputtering chamber utilized as part of a multi-chamber system, the side-loading sputtering chamber containing a plurality of co-planar, spaced-apart, radially extending, linearly elongated magnetron cathode/target assemblies each operating as a source of a sputtered target material for forming individual layers of a multilayer film on a substrate surface, and a means for serially passing a surface of a substrate over each of the cathode/target assemblies a requisite number of times for deposition of a multilayer film thereon, effectively addresses and solves problems attendant upon the use of sputtering techniques for the manufacture of, inter alia, high recording density, thin film magnetic and MO media, while maintaining full compatibility with all aspects of conventional automated manufacturing technology. Further, the means and methodology provided by the present invention enjoy diverse utility in the manufacture of other devices and products requiring multilayer thin film coatings.
An advantage of the present invention is an improved method for forming a multilayer thin film on at least one surface of a substrate.
Another advantage of the present invention is an improved method for forming a multilayer thin film with very good radial thickness uniformity over a disk-shaped substrate of wide diameter.
A further advantage of the present invention is an improved method for forming (Co/Pd)n and (Co/Pt)n multilayer superlattice structures by means of sputtering techniques.
A still further advantage of the present invention is an improved apparatus for forming multilayer thin films by sputtering.
Yet another advantage of the present invention is an improved apparatus for forming multilayer thin films on large diameter disk-shaped substrates with very good radial thickness uniformity of about +/xe2x88x923%.
Additional advantages and other features of the present invention will be set forth in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims.
According to one aspect of the present invention, the foregoing and other advantages are obtained in part by a method of forming a multilayer film on at least one surface of a substrate with improved thickness uniformity, comprising the sequential steps of:
(a) providing a vacuum chamber comprising:
(i) a pair of parallel top and bottom walls connected by at least one side wall;
(ii) at least one entry/exit means in the at least one side wall for insertion and withdrawal of a substrate from the chamber;
(iii) a plurality of spaced-apart, radially extending, linearly elongated sputtering sources arranged in a co-planar array adjacent one of the top or bottom walls of the chamber, each of the linearly elongated sputtering sources having a length and a width; and
(iv) a gripper/transporter for gripping and moving the substrate in a generally circular, planar path past each of the plurality of radially extending sputtering sources, such that the at least one deposition surface of the substrate faces each of the sputtering sources during movement along the circular path, for deposition of multilayer film thereon;
(b) inserting the substrate into the chamber via the at least one side wall entry/exit means, the at least one deposition surface of the substrate having a maximum lateral dimension less than either the length or the width of each of the linearly elongated sputtering sources;
(c) gripping the substrate at edges thereof by means of the gripper/transporter;
(d) sputtering target material from each of the plurality of sputtering sources; and
(e) moving the substrate by means of the gripper/transporter in a circular path past each of the plurality of sputtering sources and depositing on the at least one deposition surface thereof a desired multilayer film comprising a predetermined number of sub-layers.
According to an embodiment of the present invention, step (a)(i) comprises providing a generally cylindrically-shaped vacuum chamber comprising flat, circularly-shaped top and bottom walls connected by a curved side wall; step (a)(ii) comprises providing the at least one entry/exit means in the curved side wall; step (a)(iii) comprises providing at least a pair of radially extending, linearly elongated, magnetron sputtering sources adjacent the bottom wall of the chamber; and step (a)(iv) comprises providing the gripper/transporter as including a radially extending arm rotatable about an axis co-axial with that of the cylindrically-shaped chamber.
In accordance with an embodiment of the present invention, step (b) comprises inserting a disk-shaped substrate having a pair of opposed deposition surfaces, the diameter of the disk being less than the length and width of each of the sputtering sources; step (a)(iii) further comprises providing another plurality of spaced-apart, radially extending, linearly elongated sputtering sources arranged in a co-planar array adjacent the top wall of the cylindrically-shaped chamber for performing multilayer film deposition on each of the pair of deposition surfaces of the substrate.
Embodiments of the present invention comprise the further step of:
(f) removing the substrate from the chamber via the at least one entry/exit means after completion of step (e); wherein: step (a) comprises providing the vacuum chamber as part of an in-line, multi-station apparatus including at least one process module upstream of the vacuum chamber and at least one process module downstream of the vacuum chamber; step (b) comprises inserting the substrate into the vacuum chamber via a first entry/exit means which receives the substrate from an adjacent upstream process module; and step (f) comprises removing the substrate with the multilayer film thereon from the vacuum chamber via a second entry/exit means which supplies the substrate to an adjacent downstream process module.
In accordance with embodiments of the present invention, step (a)(iii) comprises providing a plurality of separately energizable sputtering sources; step (d) comprises regulating the energizing power applied to each sputtering source to provide a preselected rate of sputtering therefrom; and step (e) comprises regulating the moving speed of the substrate past the plurality of sputtering sources and selecting the number of times the substrate passes by the sputtering sources for deposition thereon of the desired multilayer film.
Embodiments of the present invention include providing in step (a)(iii) a plurality of linearly elongated, rectangularly-shaped sputtering sources each having a length of about 9 inches and a width of about 6 inches; and in step (b) a disk-shaped substrate is inserted which has a diameter of about 3.75 inches (95 mm).
According to a specific embodiment of the present invention, step (a)(iii) further comprises providing at least one pair of sputtering sources, a first one of the pair of sources being a Co source and a second one of the pair of sources being a Pd source or a Pt source; and step (e) comprises depositing on the at least one surface of the disk-shaped substrate a (Co/Pd)n or a (Co/Pt)n multilayer superlattice film, where n is an integer from about 10 to about 30, and the thickness of each of the Co and Pd or Pt sub-layers of the superlattice is from about 5 to about 8 xc3x85, with a radial thickness uniformity of about +/xe2x88x923% over the deposition surface of the 95 mm diameter disk.
According to another aspect of the present invention, an apparatus for forming a multilayer film on at least one surface of a substrate comprises a vacuum chamber including:
(a) a pair of parallel top and bottom walls connected by at least one side wall;
(b) at least one entry/exit means in the at least one side wall for insertion and withdrawal of a substrate from the chamber;
(c) a plurality of spaced-apart, radially extending, linearly elongated sputtering sources arranged in a co-planar array adjacent one of the top or bottom walls of the chamber, each of the linearly elongated sputtering sources having a length and a width; and
(d) a gripper/transporter for gripping and moving the substrate in a generally circular, planar path past each of the plurality of radially extending sputtering sources, such that the at least one deposition surface of the substrate faces each of the sputtering sources during movement along the circular path, for deposition of the multilayer film thereon.
According to embodiments of the present invention, the vacuum chamber is generally cylindrically-shaped, including flat, circularly-shaped top and bottom walls connected by a curved side wall; the at least one entry/exit means is located in the curved side wall; the plurality of sputtering sources includes at least a pair of radially extending, linearly elongated, magnetron sputtering sources adjacent the bottom wall of the chamber; and the gripper/transporter comprises a radially extending arm rotatable about an axis co-axial with that of the cylindrically-shaped chamber.
In accordance with further embodiments of the present invention, the apparatus further comprises:
(e) a substrate conveyor means for inserting a disk-shaped substrate into the vacuum chamber via the entry/exit means, the disk having a pair of opposed deposition surfaces, the diameter of the disk being less than the length and the width of each of the sputtering sources; and
(f) another plurality of spaced-apart, radially extending, linearly elongated sputtering sources arranged in a co-planar array adjacent the top wall of the cylindrically-shaped chamber for performing multilayer film deposition on each of the pair of deposition surfaces of the disk-shaped substrate.
Embodiments of the present invention include apparatus wherein the vacuum chamber forms part of an in-line, multi-station apparatus including at least one process module upstream of the vacuum chamber and at least one process module downstream of the vacuum chamber; and the side wall of the vacuum chamber comprises a first entry/exit means which receives the substrate from an adjacent upstream process module for insertion into the vacuum chamber and a second entry/exit means opposite the first entry/exit means for withdrawing the substrate from the vacuum chamber and for supplying the substrate to an adjacent downstream process module.
According to embodiments of the present invention, the plurality of sputtering sources are separately energizable, whereby the energizing power applied to each sputtering source can be regulated to provide a preselected rate of sputtering therefrom; and the gripper/transporter includes means for regulating the speed of the substrate moving past the plurality of sputtering sources in the circular path and the number of times the substrate passes by the sputtering sources for deposition thereon of the desired multilayer film.
In accordance with particular embodiments of the present invention, each of the plurality of linearly elongated, rectangularly-shaped sputtering sources has a length of about 9 inches and a width of about 6 inches; and the substrate is a disk-shaped substrate having a diameter of about 3.75 inches (95 mm).
Embodiments of the present invention include apparatus wherein the plurality of sputtering sources comprises at least one pair of sputtering sources, a first one of the pair of sources being a Co source and a second one of the pair of sources being a Pd source or a Pt source; and the multilayer film formed on the at least one deposition surface of the substrate is a (Co/Pd)n or a (Co/Pt)n multilayer superlattice film, where n is an integer from about 10 to about 30, and the thickness of each of the Co and Pd or Pt sub-layers is from about 5 to about 8 xc3x85, with a radial thickness uniformity of about +/xe2x88x923% over the deposition surface of a 95 mm diameter disk as the substrate.
According to still another aspect of the present invention, an apparatus for forming a multilayer film on at least one surface of a substrate, comprises:
a vacuum chamber including therein a plurality of co-planar, linearly elongated, radially extending sputtering sources; and
means for forming a sputter deposited multilayer film having a radial thickness uniformity of +/xe2x88x923% on a surface of a disk-shaped substrate of 95 mm diameter.
Embodiments of the invention include apparatus which further comprise means for forming the multilayer film with the radial thickness uniformity of +/xe2x88x923 % on the other surface of the disk-shaped substrate; and means for inserting and withdrawing the substrate from the vacuum chamber via a side wall of the chamber.
Additional advantages and aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein embodiments of the present invention are shown and described, simply by way of illustration of the best mode contemplated for practicing the present invention. As will be described, the present invention is capable of other and different embodiments, and its several details are susceptible of modification in various obvious respects, all without departing from the spirit of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as limitative.